1. Field of the Invention
The invention is directed to a gear unit for a compound transmission having a planetary stage by which an input shaft and an output shaft can be coupled with one another to realize different transmission ratios, wherein the planetary stage comprises at least one sun gear, at least one ring gear, and at least one planet carrier guiding a planet gear.
2. Description of the Related Art
Compound transmissions are used inter alia for agricultural and municipal utility vehicles to achieve large speed ranges at a reasonable cost. Thus the very broad spectrum of duties of an agricultural or municipal utility vehicle, e.g., the performance of work in fields and transportation, results in a wide variety of driving ranges which requires a correspondingly large spread between a slowest speed and a fastest speed. Further, transmissions in utility vehicles of this type usually require small geometric ratio steps between the individual speeds and this, combined with the large spread, results in the large number of speeds.
A compound transmission in an agricultural or municipal utility vehicle typically comprises a stepped group or main group, an upstream or downstream splitter group, a range group which is usually arranged downstream, and often also a reversing group and a creeper gear group. A gear sequence of the transmission is predefined by the main group, this gear sequence being correspondingly influenced by the further upstream and downstream transmission groups and the respective stages thereof. Thus the gear sequence of the main group is compressed by an upstream or downstream splitter group in that the gear ratio steps of the main group are divided by small ratio steps of the splitter group and the number of ratios is subsequently multiplied by the number of realizable steps of the splitter group. In contrast, a downstream range group causes a multiplication of the gear steps of the main group in different driving ranges by large ratio steps. By a reversing group which is also usually provided, a reversal of rotational direction can be realized which, in conjunction with the other transmission groups, usually also makes it possible to realize a plurality of reverse speeds. Finally, a creeper gear group is provided for the purpose of realizing a slow driving of the respective utility vehicle by an extensive reduction, for example for using in difficult terrain or for work requiring an extremely slow driving of the utility vehicle.
US2008/0245167 A1 discloses a transmission unit for a compound transmission comprising a planetary stage and forms within the compound transmission a range group downstream of the main group of the compound transmission. An input shaft of the range group and an output shaft can be coupled with one another via the planetary stage to realize different transmission ratios, this planetary stage comprising the following components: sun gear, ring gear, and a planet carrier guiding a plurality of planet gears. Of these components, the sun gear is then arranged on the input shaft and the planet carrier is coupled with the output shaft so as to be fixed with respect to rotation relative to it, while the ring gear can be fixed at a housing on the one hand and likewise coupled with the output shaft so as to be fixed with respect to rotation relative to it on the other hand for realizing the different transmission ratios.